Piston actuated rotary union

ABSTRACT

A rotary union includes a housing forming a bore and a piston bore having an open end and disposed at a radially offset distance with respect to the bore. The piston bore is fluidly isolated from the bore. A seal carrier is slidably disposed within the bore, and includes an actuation arm extending radially outwardly relative to the bore such that it overlaps the piston bore. A piston slidably disposed in the piston bore is extendible to releasably abut the actuation arm and urge the seal carrier to displace relative to the bore when the piston displaces relative to the piston bore.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/026,218, filed on Jul. 18, 2014, the contents ofwhich are hereby incorporated by reference.

TECHNICAL FIELD OF THE DISCLOSURE

The present invention relates to fluid coupling devices such as rotaryunions and, more particularly, to an improved seal control actuatormechanism that operates with fluid pressure regardless of the use oflubricating media, non-lubricating media, or no media within the rotaryunion.

BACKGROUND OF THE INVENTION

Fluid coupling devices such as rotary unions are used in industrialapplications, for example, machining of metals or plastics, workholding, printing, plastic film manufacture, papermaking, semiconductorwafer manufacture, and other industrial processes that require a fluidmedium to be transferred from a stationary source such as a pump orreservoir into a rotating element such as a machine tool spindle,work-piece clamping system, or rotating drums or cylinder. Often theseapplications require relatively high media pressures, flow rates, orhigh machine tool rotational speeds.

Rotary unions used in such applications convey fluid medium used by theequipment for cooling, heating, or for actuating one or more rotatingelements. Typical fluid media include water-based liquids, hydraulic orcooling oils, and air. In certain instances, for example, whenevacuating media from a fluid passage, rotary unions may operate undervacuum. Machines using rotary unions typically include precisioncomponents, such as bearings, gears, electrical components, and others,that are expensive and/or difficult to repair or replace during service.These components are often subject to corrosive environments or todamage if exposed to fluid leaking or venting from the rotary unionduring operation.

A rotary union typically includes a stationary member, sometimesreferred to as the housing, which has an inlet port for receiving fluidmedium. A non-rotating seal member is mounted within the housing. Arotating member, which is sometimes referred to as a rotor, includes arotating seal member and an outlet port for delivering fluid to arotating component. A seal surface of the non-rotating seal member isbiased into fluid-tight engagement with the seal surface of the rotatingseal member, generally by a spring, media pressure, or other method,thus enabling a seal to be formed between the rotating and non-rotatingcomponents of the union. The seal permits transfer of fluid mediumthrough the union without significant leakage between the non-rotatingand rotating portions. Fluid medium passing through the rotary union maylubricate the engaged seal surfaces to minimize wear of the sealmembers. When a rotary union is used with non-lubricating media (such asdry air) or without any media, the engaged seal surfaces can experiencea “dry running” condition, which causes rapid seal wear due to lack ofadequate lubrication. Extended periods of dry running can cause severedamage to the seal members, thereby requiring expensive andtime-consuming replacement of one or both seal members.

High-speed machining equipment, such as computer-numerical-control (CNC)milling machines, drilling machines, turning machines, transfer lines,and so forth, use rotary unions to supply a medium directly to thecutting edge of a tool for cooling and lubrication in an arrangementthat is commonly referred to as “through spindle coolant.” A throughspindle coolant arrangement extends the service life of costly cuttingtools, increases productivity by allowing higher cutting speeds, andflushes material chips that can damage the work-piece or cutting toolaway from the cutting surfaces of the tool. Different work-piecematerials typically require different media for optimal productivity andperformance. For example, air or aerosol media may provide betterthermal control when machining very hard materials, while liquidcoolants may offer better performance when machining softer materials,such as aluminum. In addition, certain kinds of work may be performedmore effectively and less expensively without a through-spindle medium.

In certain applications, it may also be desired to avoid any spillage ofthe working fluid of the coupling when the seal is disengaged, forexample, when changing tool spindles. Along these same lines, it mayfurther be desired to engage the rotary seal of the coupling before theworking fluid is at full pressure so that the initiation of flow, whichflow may include a mixture of the working fluid with air, does not causeleakage of the working fluid.

BRIEF SUMMARY OF THE DISCLOSURE

In one aspect, the disclosure describes a rotary union. The rotary unionincludes a housing having a bore in fluid communication with a mediachannel opening and a piston bore having an open end disposed at aradially offset distance with respect to the bore. The piston bore isfluidly isolated from the media channel opening and the bore, and isfluidly connected to an actuation port. A non-rotating seal carrier isslidably disposed within the bore, and the housing has a media channelin fluid communication with the bore. An actuation arm is connected tothe non-rotating seal carrier and extends radially outwardly therefromwith respect to the bore. The actuation arm at least partially overlapsthe open end of the piston bore. A piston is slidably disposed withinthe piston bore such that a variable piston volume is defined betweenthe piston and the piston bore. The variable piston volume is fluidlyconnected to the actuation port, and the piston is adapted to extend outfrom the open end of the bore when a fluid pressure provided via theactuation port is present in the variable piston volume. The piston isconfigured to releasably abut the actuation arm and to urge theactuation arm, and thus the non-rotating seal carrier, to displacerelative to the bore when the piston displaces relative to the pistonbore. A seal is disposed around the non-rotating seal carrier to createa sliding seal between the non-rotating seal carrier and the bore. Thenon-rotating seal carrier is arranged to extend relative to the housingwhen the fluid under pressure is present in the piston bore.

In another aspect, the disclosure describes a method for operating arotary union. The method includes providing a housing having a bore influid communication with a media channel opening and a piston borehaving an open end disposed at a radially offset distance with respectto the bore, the piston bore being fluidly isolated from the mediachannel opening and the bore and fluidly connected to an actuation port.The method further includes slidably disposing a non-rotating sealcarrier within the bore in the housing, and fluidly connecting a mediachannel with the bore. An actuation arm connected to the non-rotatingseal carrier and extending radially outwardly therefrom with respect tothe bore is provided such that the actuation arm at least partiallyoverlaps the open end of the piston bore. A piston is slidably disposedwithin the piston bore such that a variable piston volume is definedbetween the piston and the piston bore. The method also includesapplying an actuation fluid pressure at the actuation port such that theactuation fluid pressure is present in the variable piston volume toprovide a pneumatic force tending to extend the piston relative to thepiston bore, and pushing the actuation arm with the piston and urgingthe actuation arm, and thus the non-rotating seal carrier, to displacerelative to the bore when the piston displaces relative to the pistonbore.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a front view of a non-rotating portion of one embodiment of arotary union in accordance with the disclosure.

FIGS. 2, 3 and 7 are cross sections of the embodiment of a rotary unionshown in FIG. 1 in two operating positions.

FIGS. 4 and 5 are cross sections of a second embodiment of a rotaryunion in two operating positions.

FIG. 6 is a flowchart for a method of operating a rotary union inaccordance with the disclosure.

FIG. 8 is a cross section of an alternative embodiment of a rotary unionin accordance with the disclosure.

DETAILED DESCRIPTION

In the drawings, which form a part of this specification, FIG. 1 is afront view of a non-rotating portion 101 of the rotary union 100. FIGS.2 and 3 are cross sections of the rotary union 100 in two operatingpositions. In reference to FIGS. 1-3, the rotary union 100 includes arotating seal member 102 connected to the end of a rotating seal carrier103, which is commonly referred to as a rotor, and a non-rotating sealmember 104 that is connected at the end of a non-rotating seal carrier105. The non-rotating seal carrier 105 is axially moveable relative to ahousing 106, which is best shown in FIGS. 2 and 3. Although the housing106 is shown as a two-piece construction in FIGS. 2 and 3, a singlepiece construction, or a construction of more than two pieces may beused as desired for the housing 106. In the present disclosure, thehousing 106 is referred to as a single structure without regard to thenumber of pieces that make up its construction. The rotating seal member102 is associated with a rotating machine component (not shown) such asa machine spindle, as is known. The housing 106 is associated with anon-rotating machine component (not shown). A segmented conduit or mediachannel 112 extends through the rotating seal carrier 103, thenon-rotating seal carrier 105, and the rotating and non-rotating sealmembers 102 and 104 respectively, as best illustrated in FIGS. 2 and 3.

Portions of the media channel 112 are defined in different components ofthe rotary union 100 to provide a fluid passageway through the rotatingand non-rotating carriers 103 and 105 when the rotating and non-rotatingseal members 102 and 104 are engaged. The media channel 112 may beselectively arranged to sealingly enclose fluids when the rotating andnon-rotating seal members 102 and 104 are engaged to one another, and beopen for venting to the atmosphere when the rotating and non-rotatingseal members 102 and 104 are not engaged, as is described in more detailrelative to the operation of the rotary union 100 and the descriptionthat follows relative to the flowchart of FIG. 6, described below. Incertain applications, the media channel 112 may be subjected to a vacuumthat pulls and evacuates working fluids from within the media channel112.

The rotating seal carrier 103, which can be connected or associated withany type of machine component such as a spindle on a CNC millingmachine, supports the rotating seal member 102. A mechanical face sealis created when the rotating seal member 102 is engaged with thenon-rotating seal member 104. The mechanical face seal operates to sealthe media channel 112 for transferring a fluid medium from thenon-rotating to the rotating seal carriers 103 and 105 and, thus,through corresponding machine components to which the carriers areconnected. In the illustrated embodiment, the housing 106 is connectableto a non-rotating portion or component of a machine by bolts (fourshown) extending through bolt holes 109 to engage corresponding threadedopenings formed in the non-rotating machine component, but othermounting arrangements can be used.

The rotating machine component may form a bore that sealably engages anouter seal 111 disposed around a portion of the housing 106, as shown inFIGS. 2 and 3. Similarly, a bore formed in the rotating machinecomponent may sealably engage an outer rotating seal 113 disposed arounda portion of the rotating seal carrier 103. In the illustratedembodiment, a secondary seal 114 is disposed between the housing 106 andthe non-rotating seal carrier 105. The secondary seal 114 slidably andsealably engages the non-rotating seal carrier 105 to provide a sealingfunction between the non-rotating seal carrier 105 and the housing 106during operation. As shown in the sections of FIGS. 2 and 3, thesecondary seal 114 is represented generically having a rectangularsection. It is contemplated that the secondary seal 114 can be embodiedas any appropriate type of sliding seal, for example, a U-cup seal,O-ring seal, lip seal and the like. When pressurized media or a vacuumis present within the media channel 112, the secondary seal 114 acts toseal the media channel 112 from the environment and other portions ofthe rotary union 100.

In the embodiment for the rotary union 100 shown in the cross section ofFIGS. 2 and 3, the non-rotating seal member 104 is connected to thenon-rotating seal carrier 105. The non-rotating seal carrier 105 isslidably and sealably disposed within a bore 128 of the housing 106, andhas an outer diameter portion that slidably engages a land 129 of thebore 128. The bore 128 is generally cylindrical and may form a slightgap between an inner diameter thereof and an outer diameter of thenon-rotating seal carrier 105 to allow for angular mis-alignment in anaxial direction between the non-rotating seal carrier 105 and the bore128, which advantageously permits the rotary union to accommodateassembly and operational misalignment conditions between rotating andnon-rotating machine components. The axial length and inner diameterdimension of the land 129, which extends annularly around thenon-rotating seal carrier 105, can be selected depending on theparticular design requirements and expected misalignment betweencomponents for each application. The structural arrangement permittingsliding of the non-rotating seal member 104 relative to the housing 106enables the selective engagement and disengagement of the non-rotatingseal member 104 with the rotating seal member 102, and compensates foraxial displacement that may be present as between the two seal members102 and 104.

In the illustration of FIG. 2, the seal members 102 and 104 are shown ina disengaged position in which the non-rotating seal carrier 105 isretracted within the bore 128 relative to the housing 106. In theillustration of FIG. 3, the seal members 102 and 104 are shown in anengaged position in which the non-rotating seal carrier 105 is extendedwithin the bore 128 relative to the housing 106. In the engagedposition, a mechanical face seal is formed at or around an interface 125between the rotating and non-rotating seal members 102 and 104.

The housing 106 has passages and openings for provision of a workingfluid to the media channel 112, which may be a liquid or a gas, and forprovision of air or a vacuum to an activation channel, which causes thenon-rotating seal carrier 105 to move relative to the housing 106. Morespecifically, the housing 106 forms an actuation port 200, which isfluidly connected to a piston bore 202 formed in the housing 106. Thepiston bore 202 has a centerline 203 that extends parallel to acenterline 205 of the bore 128, as shown in FIGS. 2 and 3, at an offsetdistance, D (denoted in FIG. 3), therefrom.

A floating piston 206 is slidably disposed within the piston bore 202.The floating piston 206 has a generally cylindrical shape that freelyand generally sealably moves within the piston bore 202. In theillustrated embodiment, air or another fluid at a pressure applied atthe actuation port will fill the piston bore and induce a pneumatic (or,hydraulic, depending on the type of fluid used) force onto an axial faceof the piston 206 tending to push the piston 206 in an outward orextending direction relative to the housing 106. A vacuum may also beapplied to retract the piston 206 into the bore 202. During operation, aforce tending to extend the piston 206 relative to the housing 106 istransferred to the non-rotating seal carrier 105. In the particularembodiment shown, the non-rotating seal carrier 105 forms, or isconnected to, an actuation arm 208 that extends radially outwardly fromthe non-rotating seal carrier 105 relative to the bore centerline 205.The actuation arm 208 is contacted by an axially-outward face 210(denoted in FIG. 3) of the piston 206 and is pushed thereby while thepiston 206 is urged to extend, and extends, relative to the housing 106as described above. In the illustrated embodiment, the arm 208 isslidingly accepted within a slot or channel 207 formed in the housing106. The arm 208 and slot 207 together form a keyed arrangement thatprevents rotation of the non-rotating seal carrier 105 during operation.

Additional force components or force contributions may affect a netforce tending to extend or translate the non-rotating seal carrier 105relative to the housing 106. For example, a spring (not shown), may beadded between the non-rotating seal carrier 105 and the housing 106tending to bias the non-rotating seal carrier 105 either toward or awayfrom the housing 106. In one embodiment, for example, such a spring maybe placed within the bore and connected between the piston and housingto provide a force therebetween that biases the piston either away ortowards the housing. Additionally, the non-rotating seal carrier 105 maypresent a net hydraulic surface, which can also be referred to as abalance ratio, that is exposed to fluid pressure within the mediachannel 112 and which yields a force tending to urge the non-rotatingseal carrier 105 to move in the presence of fluid within the mediachannel 112.

The size or dimension of a clearance between the piston 206 and the bore202, which facilitates the free motion of the piston 206 within the bore202, may be controlled in a fashion that is similar to the sealsprovided between a bore and a reciprocating piston in an internalcombustion engine to permit at least some leakage of fluid from withinthe bore 202 to the environment. Such leakage may help to discouragesticking or binding of the piston 206 within the bore 202 duringoperation.

During operation, the application of a relatively low air pressure tothe piston bore 202 will cause the non-rotating seal carrier 105 toextend relative to the housing 106. In other words, notwithstanding anyhydraulic forces acting on the non-rotating seal carrier 105 by themedia and causing the same to axially move relative to the housing 106,an application of air pressure to the piston bore 202 will have theeffect of a pneumatic (or hydraulic, depending on the type of fluidused) linear piston actuator that uses the piston 206 to push againstthe arm 208 and extend the non-rotating seal carrier 105 relative to thebore 202 of the housing 106. Specifically, when an air flow is providedto the air actuation port 200, the flow momentum and pressure of thatair will fill the piston bore 202 and, even though some of the air mayleak through the gap between the piston 206 and bore 202, it willdynamically and pneumatically push against a back side of the piston206, thus causing the non-rotating seal carrier 105 to move in anextending direction relative to the housing 106. Put another way, axialmotion of the rotor or rotating seal carrier 103 towards the housing 106may be prevented while air pressure is present within the piston bore202. A snap ring 212 may be connected to the housing 106 and arranged tolimit the axially outward motion of the non-rotating seal carrier 105relative to the housing 106 by contacting the arm 208 through the end ofthe slot 207 when the non-rotating seal carrier 105 is in a fullyextended position, as shown in FIG. 3.

In one aspect, the rotary union 100 is configured to prevent undesiredforces acting on the non-rotating seal carrier 105 in the event ofpartial or complete failure of the secondary seal 114 during operation.For example, a partial or complete failure in the sealing function ofthe secondary seal 114 may result in media present within the mediachannel 112 passing along the land 129 of the bore 128 and into thevicinity of the piston 206. If a sufficient amount of media can collectand pressurize around the piston 206, it may impart a hydraulic forceonto the piston and, thus, onto the non-rotating seal carrier 105.Moreover, such fluid may further intrude into the pneumatic system thatis connected to the air actuation port 200. To avoid such effects in theevent of leakage, the rotary union 100 includes a fluid ventingarrangement, as is shown in the cross section of FIG. 7.

In reference to FIG. 7, the housing 106 forms a collection channel 214,which in the illustrated embodiment is disposed within the bore 128 suchthat the secondary seal 114 is between the collection channel 214 and afluid inlet side of the media channel 112. The collection channel 214extends annularly around an entire cross section of the bore 128. Inthis arrangement, fluid from within the media channel 112 that may leakpast the secondary seal 114 will collect within the collection channel214. At least one vent passage 216 is formed in the housing 106. In theillustrated embodiment, two vent passages 216 are shown. Each ventpassage 216 extends entirely through the housing 106 between thecollection channel 214 and an outer portion of the housing 106 so thatany fluid present within the collection channel 214 can exit the rotaryunion 100 through the vent passage 216. Depending on the installationorientation of the rotary union, fluid may pass through the vent channelby force of gravity or by displacement of fluid as additional fluid maybe added into the collection channel. Notably, presence of the ventpassage ensures that no leaked fluid pressurization may occur within therotary union, which may affect operation of the rotary union aspreviously described.

An alternative embodiment of the rotary union 100 is shown in FIGS. 4and 5. Here, like reference numerals denote like structures aspreviously described and shown, for example, in FIGS. 2 and 3, forsimplicity. In this embodiment, a rotary union 300 includes a secondpiston 306 that pushes against a second arm 308 formed on or connectedto the non-rotating seal carrier 105. The second piston 306 is disposedin a second bore 302 formed in the housing 106. The second bore 302 isparallel to the bore 202 that accommodates the first piston 206, asdescribed above, such that both pistons 206 and 306 can impart a forcein a single direction onto the non-rotating seal carrier 105. In theillustrated embodiment, the pistons 206 and 306 are of the sameconstruction, i.e., of identical size and shape, and are subject to thesame or a common source of pneumatic pressure during operation. Asshown, a combined air passage 312 formed in a non-rotating machinecomponent 314 into which the housing 106 is connected, is fluidlyconnected to an annular channel 310 defined between a channel formed inthe housing 106 and a surface of the machine component 314. The annularchannel fluidly interconnects the combined air passage 312 with thefirst and second bores 202 and 302 such that air pressure applied to thecombined air channel is distributed equally to the first and secondbores 202 and 302.

In a fashion similar to the first piston 206 that bears against the arm208, the second piston 306, which floats in the respective second bore302, bears against the second arm 308 and operates to push the same, andalso the non-rotating seal carrier 105, when an air pressure is presentwithin the second bore 302. In this configuration using two pistons, theforce with which the pistons urge the non-rotating seal carrier 105 inan extending direction relative to the housing 106 can be doubled whencompared with the extending force applied by a single piston of the samesize, as in the rotary union 100 described above. Additionally, twopistons, as is the case in the illustrated embodiment, or more than twopistons can be used. The two or more pistons may be symmetricallyarranged around the non-rotating seal carrier 105 to apply forcessymmetrically to the non-rotating seal carrier and thus diminish oravoid misalignment of the non-rotating seal carrier relative to the boreof the housing in which it is slidably disposed.

A flowchart for a method of operating the rotary union 100 or 300 isshown in FIG. 6. The described method is presented to illustrate onepossible mode of operating rotary unions in accordance with the presentdisclosure, and should not be understood to be exclusive of otheroperating modes or exhaustive of all possible operating modes. Thedescribed method includes desirable features for the operation of arotary union, all or a subset of which may be used at different timesduring operation or in different applications depending on theparticular requirements of each operating task.

The described method is applicable to the use of a rotary coupling in amachine tool, where undesirable operational characteristics may bepresent at the beginning and at the end of a work task. The work taskcontemplated may include a cycle of initiation, use, and evacuation ofthe working media from within the rotary union. In the contemplatedapplication, leakage of the working media is undesired both at thebeginning and at the end of the work task, when the face seals areengaging and disengaging, respectively.

With the foregoing in mind, an air flow is applied to the air actuationport at 402, which operates to engage the rotary seal in the absence ofworking media as previously discussed. For example, the air flow may beapplied to the air actuation port 200 or 310 to urge the respectivepiston(s) against the arms of the non-rotating seal carrier and push thesame, thus extending the non-rotating seal carrier relative to thehousing to engage the mechanical face seal between the rotating andnon-rotating seal members 102 and 104. When the seal has engaged, theair flow may be optionally discontinued at 404, which in one embodimentoccurs at the same time or shortly follows initiation of the media flowin the media channel at 406. It should be appreciated that for thoserotary union embodiments that include an opening spring, discontinuationof the air flow in the absence of working media may cause the seal todisengage and, thus, for those embodiments, process step 404 may beomitted. For those embodiments that do not include an opening spring,discontinuation of the air flow may not cause the seal to disengage ifstatic forces, such as friction, and closing forces, such as springs,etc., can overcome any opening forces such that seal engagement may bemaintained.

With the rotary seal engaged, a flow of working media may be initiatedat 406. Closure of the seal prior to initiation of working media flowmay be desirable for various reasons. For example, even thoughincompressible working media will cause seal engagement based on thebalance ratio of the rotary union, insufficient hydraulic forces duringa limited period of flow initiation within the media channel may permitfluid leakage unless the seals are already engaged. By first providingthe air flow to engage the seal at 402, one may ensure against suchundesirable fluid leakage.

When the work task is complete, an air flow may be applied to the airactuation port at 408. Ordinarily, the force tending to engage the sealsmay not be compounded with a hydraulic force from the working media toreduce seal wear. Here, the application of the air flow is for a limitedtime while the working fluid flow and pressure are reduced so that theseal may remain in an engaged condition. Optionally, a vacuum may beapplied to the media channel to remove any remaining working fluid at410, while the air flow is still applied to maintain the seal in anengaged condition. In this way, effective evacuation of the mediachannel can be achieved and fluid leakage can be avoided.

When evacuation of the working fluid is complete, the air flow to theair actuation port is discontinued and may optionally be replaced by theapplication of a vacuum at that same port at 412. As previouslydescribed, application of vacuum to the air actuation port may cause aretraction of the piston(s) within the respective piston bore(s), whichcan remove impediments for seal disengagement as well as operate toclean the bore from any fluids and/or other debris that may havecollected therein. It should be appreciated that this process step maynot be required if an opening spring is used to urge the seal membersapart. Alternatively, disengagement of the seal members can beaccomplished by axial motion of the rotating seal member.

In operation, the rotary union 100 or 300 may use an air flow or aliquid coolant flow provided at just above atmospheric pressure to thepiston bore(s) such that the seal members 102 and 104 can be engaged.The magnitude of the various relevant parameters, and the dimensions ofthe associated structures, may change depending on the particulardimensions that are selected for the structures that facilitate theengagement or disengagement of the seals.

A cross section of an alternative embodiment of a rotary union 500 isshown in FIG. 8, in which structures and features that are the same orsimilar to corresponding structures and features of the rotary union 100previously described are denoted by the same reference numeralspreviously used for simplicity. It is noted that the cross section ofFIG. 8 has been taken in the same orientation as the cross section shownin FIG. 7, but in the corresponding union 500. As can be seen whencomparing FIGS. 7 and 8, the rotary union 500 is generally similar tothe rotary union 100, but with structural differences as discussedbelow.

One structural difference in the rotary union 500 is in the additionalventing openings 502 (two shown), which are disposed in fluidcommunication with the vent passages 216 and extend perpendicularthereto, as shown, along a centerline of the media channel 112. Theadditional venting openings 502 facilitate venting or drainage of fluidfrom the collection channel 214 when the rotary union 500 operates inany orientation. Additionally, a ledge 504 is formed in the housing 106that serves to both reduce the mass of the housing 106, as compared tothe housing 106 of the embodiment shown in FIG. 7, as well as to providea more ready avenue for fluid venting or draining from the additionalventing openings 502.

With respect to providing a mechanical stop to limit extension of thenon-rotating seal carrier 105 with respect to the housing 106, therotary union 500 includes a collar 506 that forms a radially-outwardlyextending flange 508. The collar 506 in the illustrated embodiment ispress-fit into an end of the non-rotating seal carrier 105 such that theflange 508 protrudes outwardly from an end of the non-rotating sealcarrier 105. In the illustrated embodiment the bore 128 has a steppedportion 510 that is disposed radially outwardly with respect to the land129 of the bore 128 and that accommodates therein the flange 508 with aclearance fit. During operation, when the non-rotating seal carrier 105extends with respect to the housing 106 as it slides along the bore 128,the travel or displacement of the non-rotating seal carrier 105 alongthe bore 128 is limited and the sliding motion arrested when the flange508 abuts a radially extending annular face 512 that extends between thestepped portion 510 and the land 129 of the bore 128. The collar 506 andflange 508 are thus an alternative to the snap ring 212 shown in FIG. 2.Whether the collar 506 and flange 508, the snap ring 212, or any othermechanical stop is/are used to limit displacement of the non-rotatingseal carrier 105 with respect to the housing 106, such displacementlimitation ensures that the floating piston remains slidably supportedwithin the piston bore as the non-rotating seal carrier reaches itsmaximum extension position with respect to the housing.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

The invention claimed is:
 1. A rotary union, comprising: a housinghaving a bore in fluid communication with a media channel opening and apiston bore having an open end disposed at a radially offset distancewith respect to the bore, the piston bore being fluidly isolated fromthe media channel opening and the bore, and is fluidly connected to anactuation port; a non-rotating seal carrier slidably disposed within thebore in the housing and having a media channel in fluid communicationwith the bore; an actuation arm connected to the non-rotating sealcarrier and extending radially outwardly therefrom with respect to thebore, the actuation arm at least partially overlapping the open end ofthe piston bore; a piston slidably disposed within the piston bore andbeing unattached from the housing and actuation arm such that the pistoncan freely move axially within the piston bore independently from thehousing and the non-rotating seal carrier during operation to define avariable piston volume between the piston and the piston bore, thevariable piston volume being fluidly connected to the actuation port,the piston being adapted to extend out from the open end of the borewhen a fluid pressure provided via the actuation port is present in thevariable piston volume, the piston having an axially-outward face thatcontacts the actuation arm and being configured to releasably abut theactuation arm and to urge the actuation arm, and thus the non-rotatingseal carrier, to displace relative to the bore when the piston displacesrelative to the piston bore; and a seal disposed around the non-rotatingseal carrier and disposed to create a sliding seal between thenon-rotating seal carrier and the bore; wherein the non-rotating sealcarrier is arranged to extend relative to the housing when the fluidpressure is present in the piston bore.
 2. The rotary union of claim 1,further comprising a collection channel formed in the housing around thebore and in fluid communication with the bore, the collection channeldisposed between the seal and an open end of the bore opposite the mediachannel opening, the collection channel extending annularly around anentire cross section of the bore and adapted to collect a media fluidleakage past the seal.
 3. The rotary union of claim 2, furthercomprising at least one vent passage that is formed in the housing andextending from the collection channel entirely through the housing to anouter portion of the housing, the at least one vent passage beingadapted to vent fluid present or collected within the collection channelout of the housing.
 4. The rotary union of claim 1, further comprising amechanical stop that limits a displacement of the non-rotating sealcarrier with respect to the housing in an extending direction.
 5. Therotary union of claim 4, wherein displacement of the non-rotating sealcarrier is limited such that the piston remains slidably supportedwithin the piston bore.
 6. The rotary union of claim 4, wherein themechanical stop includes a snap ring installed in a groove formed in thehousing around a free end of the non-rotating seal carrier, the snapring abutting the actuation arm when the non-rotating seal carrier isextended relative to the housing.
 7. The rotary union of claim 1,wherein the bore is generally cylindrical and forms a gap between aninner diameter of the bore and an outer diameter of the non-rotatingseal carrier, the gap being configured to allow for angular misalignmentin an axial direction between the non-rotating seal carrier and thebore, which advantageously permits the rotary union to accommodateassembly and operational misalignment conditions between rotating andnon-rotating machine components.
 8. The rotary union of claim 7, whereinthe non-rotating seal carrier and the bore, are slidably associatedalong a cylindrical land surface having an axial length along the bore,the axial length and inner diameter dimension of the cylindrical landsurface being configured to accommodate misalignment between thenon-rotating seal carrier and the bore.
 9. The rotary union of claim 1,wherein the piston is a floating piston having a clearance fit with thepiston bore such that a leakage of actuating fluid provided to thepiston bore is present during operation.
 10. The rotary union of claim1, wherein a clearance between the piston and the piston bore isconfigured to permit at least some leakage of fluid from within thepiston bore at times when the fluid pressure is present at the actuationport and the variable piston volume.
 11. The rotary piston of claim 10,wherein when the fluid pressure is present in the variable pistonvolume, the fluid pressure is arranged to impart a pneumatic force on aback side of the piston that is exposed to the variable piston volume.